Wednesday, April 3 Warm-up: Agenda: Get a lab from the counter. Read it. Agenda: PowerPoint / Notes Virtual Lab Study Time ….1

The Buoyant Force 2 Can you float? Why do objects float? 2 The Buoyant Force Can you float? Think about you in a pool . . . Gravity is pulling you down, what keeps you floating? A force called the buoyant force. The buoyant force is an upward force that is exerted by a fluid on any object in the fluid.

What causes the buoyant force? Why do objects float? 2 What causes the buoyant force? The buoyant force is caused by the pressure that is exerted by a fluid on an object in the fluid. The force that is exerted on the cube due to water pressure is not balanced, and a net upward force is acting on the cube due to the pressure of the water.

Why do objects float? 2 Sinking and Floating The buoyant force pushes an object in a fluid upward, but gravity pulls the object downward. If the weight of the object is greater than the buoyant force, the net force on the object is downward and it sinks. If the buoyant force is equal to the object’s weight, the forces are balanced and the object floats.

Changing the Buoyant Force Why do objects float? 2 Changing the Buoyant Force Whether an object sinks or floats depends on whether the buoyant force is smaller than its weight. The weight of an object depends only on the object’s mass, which is the amount of matter the object contains. The weight does not change if the shape of the object changes.

Buoyant Force and Shape Why do objects float? 2 Buoyant Force and Shape Buoyant force does depend on the shape of the object. The fluid exerts upward pressure on the entire lower surface of the object that is in contact with the fluid.

Buoyant Force and Shape Why do objects float? 2 Buoyant Force and Shape If this surface is made larger, then more upward pressure is exerted on the object and the buoyant force is greater.

Archimedes’ Principle Why do objects float? 2 Archimedes’ Principle According to Archimedes’ principle, the buoyant force on an object is equal to the weight of the fluid it displaces. According to Archimedes’ principle, the weight of the overflow, or displaced water, would by equal to the buoyant force on the object, and therefore equal to the weight of the object.

Archimedes’ Principle Why do objects float? 2 Archimedes’ Principle Virtual Lab: Why do things float?

Tuesday, April 3 Warm-up: Agenda: Get a worksheet from the counter and complete it. You may use your book / notebook for help. Turn it in when you are finished. Agenda: Bill Nye on Buoyancy Video Boats Notes ….1

Why do objects float? 2 Boats Archimedes’ principle provides another way to understand why boats that are made of metal can float. According to Archimedes’ principle, increasing the weight of the water that is displaced increases the buoyant force. By making the volume of a boat large enough, enough water can be displaced so that the buoyant force is greater than the weight of the steel.

Why do objects float? 2 Boats Even though the boat and the cube have the same mass, the boat displaces more water because of its shape. Therefore the boat floats, but the cube sinks.